Display devices have typically used cathode-ray tubes (CRT). Presently, much effort has been made to study and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDP), field emission displays, and electro-luminescence displays (ELD), as a substitute for CRT. LCD devices have advantages over the other flat panel displays, some of the advantages are high resolution, light weight, thin profile, compact size, and low power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other. A voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
Because the LCD device is a non-emissive type display device, a backlight is needed to supply the non-emissive type display device with light.
FIG. 1 is an exploded perspective view illustrating an LCD module according to the related art, and FIG. 2 is a cross-sectional view illustrating the LCD module of FIG. 1.
Referring to FIGS. 1 and 2, an LCD module 1 includes a liquid crystal panel 30, a backlight unit 20, a main supporter 10, a bottom cover 40 and a top cover 50.
The backlight unit 20 and the liquid crystal panel 30 are sequentially located over a bottom cover 40. The main supporter 10 has a rectangular frame shape and supports the backlight unit 20 and the liquid crystal panel 30. The main supporter 10 is combined with the bottom cover 40. The top cover 50 is disposed on the top of the LCD module 1. The top cover 50 presses and fixes a peripheral portion of the liquid crystal panel 30 and is combined with the main supporter 10 and the bottom cover 40.
A printed circuit board (PCB) 34 as a driving circuit of the liquid crystal panel 30 is connected to the liquid crystal panel 30 through a plurality of tape carrier package (TCP) films 32 which are flexible. The PCB 34 has a plurality of output pads and dummy output pads 35 in a pad portion PA. The TCP film 32 has a plurality of input pads and output pads. The liquid crystal panel 30 has a plurality of input pads. The output pad of the PCB 34 is connected to the input pad of the TCP film 32, and the output pad of the TCP film 32 is connected to the input pad of the liquid crystal panel 30. The dummy pads 35 are located between the output pads of the PCB 34.
To connect the output pad of the PCB 34 to the input pad of the TCP film 32, an anisotropic conductive film (ACF) is used. The ACF includes a bonding material and a plurality of conductive particles in the bonding material. The ACF is formed entirely in the pad portion PA. To improve bonding efficiency between the PCB 34 and the TCP film 32, the same output pad structure in the PCB 34 is formed, and to do this, the dummy output pads 35 are formed.
The backlight unit 20 includes a backlight 24, a reflecting sheet 22, a light guide plate 26, and optical sheets 28 such as a prism sheet and a diffusion sheet. A lamp 24 is used as the backlight 24, and the lamp 24 is located at a side portion of the LCD module 1. The lamp 24 is guided by a lamp guider (not shown) that partially covers the lamp 24. The lamp 24 is fixed by a couple of lamp holders that are located at both ends of the lamp 24.
A cover shield 60 is located below the bottom cover 40 and covers the PCB 34 and a lamp driving circuit.
Referring to FIG. 2, when modulizing the LCD module 1, for space efficiency, the PCB 34 is located below the bottom cover 40. To connect the PCB 34 at a bottom portion and the liquid crystal panel 40 at a top portion, the TCP film 32 is bent, for example, twice. The cover shield 60 has an embossing pattern 63 at an inner surface of the cover shield 60. The embossing pattern 63 faces and is spaced apart from the PCB 34.
FIG. 3 is a view illustrating relationship of dummy output pads of a PCB and embossing patterns of a cover shield according to the related art, and FIGS. 4A and 4B are cross-sectional views, taken along a line IV-IV, illustrating states that an external pressure is not applied to a cover shield and applied to the cover shield, respectively.
Referring to FIG. 3, embossing patterns 63 correspond to a pad portion PA at a periphery of a PCB 34. Most of the embossing patterns 63 correspond to dummy output pads 35. An ACF 70 is formed entirely on the pad portion PA. A first portion of the ACF 70 connects an output pad 36 of the PCB 34 to an input pad of the TCP 32. A second portion of the ACF 70 located on the dummy pads 35 is exposed.
The output pads 36 and the dummy output pads 35 of the PCB 34 are connected to a PCB ground portion (not shown) to ground them. For example, all the pads 36 and 35 are connected to a ground line in the PCB 34 to ground them. To strengthen ground, the PCB ground portion is connected to at least one of other components of the LCD module made of metal which can act as other ground portion. For example, at least one or combination of a bottom cover (40 of FIGS. 1 and 2), a top cover (50 of FIGS. 1 and 2), a cover shield 60 and so on can be used as the other ground portion. To prevent electromagnetic interference (EMI), resistance, for example, of several ohms between the PCB ground portion and the other ground portion is needed. To do this, a resistor chip having several ohms may be used between the PCB ground portion and the other ground portion, and thus a predetermined ground state preventing EMI is obtained.
Referring to FIG. 4A, when an external pressure is not applied to the cover shield, a distance between the embossing pattern 63 and the second portion of the ACF 70 remains.
Referring to FIG. 4B, when an external pressure is applied to the cover shield, the embossing pattern 63 moves downward and presses the ACE 70. Accordingly, the embossing pattern 63 is electrically connected to the dummy output pad 35 through conductive particles 72 of the ACF 70. Due to such the unexpected connection, resistance between the PCB ground portion and the cover shield usable as the other ground portion is about 0 ohm, and thus the predetermined ground state in the PCB changes. Accordingly, there may occur EMI, and display quality is reduced.